The present invention relates to a laser machining apparatus and, more particularly, to a laser machining apparatus of the type using a mask generator which predetermines a shape to be produced by a laser beam.
Generally, a laser machining apparatus comprises a laser for emitting a laser beam having a high energy density, an optical system for projecting the laser beam onto a workpiece in a desired shape, and a work table movable to cause the shaped laser beam to impinge on a desired point of the workpiece.
It has been customary in this type of laser machining apparatus to use the laser beam without any modification or after passing it through a mask, which may be prepared by punching a metal sheet to form an aperture or a slit representative of a symbol and/or a character pattern, to set up a specific configuration for illumination. For example, in an ordinary laser machining apparatus such as a laser repairer or a scriber, use is made of a mask generator having an aperture whose width is mechanically variable or a mask generator which is a combination of metal plates formed with rectangular and circular apertures. The former, for example, is described in an article entitled "Laser Application to Metal-Photo-Mask Repair" by Shogo Yoshikawa and Ryuji Tatsumi, appearing in TECNOCRAT, Vol. 12, No. 2, pages 1-5, Feb. 1979. In this article, an aperture formed in a mask generator is disposed in the path of a laser beam to shape or restrict the laser beam. The so restricted laser beam, or an image of the aperture, is focused by an object lens onto the surface of a workpiece.
A laser machining apparatus generally called a "marker" has been marketed which uses the above-described imaging system and scribes numerals, characters and symbols utilizing at least a single laser beam illumination. A mask generator employed with such a marker comprises metal plates which are punched in to shape of various kinds of numerals and characters, the metal plates being combined to scribe various kinds of inscription. The drawback encountered with such a marker is that various kinds of inscriptions are unattainable unless the marker is furnished with a large number of masks. Another drawback is that the metal plate has to be replaced with another by an awkward procedure every time the inscription is changed and, moreover, replacing the metal plate by hand is dangerous due to the use of a high output laser. Additionally, mask replacement requires the production line to be halted, resulting in reduced throughput.